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Extremely Sensitive, Fast Measurement of PFAS with Iodide CI-TOFMS


Gas-Phase Detection of Fluorotelomer Alcohols and Other Oxygenated Per- and Polyfluoroalkyl Substances by Chemical Ionization Mass Spectrometry 

Riedel et al.  
DOI: 10.1021/acs.estlett.9b00196
Environmental Science and Technology Letters, 2019 

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent environmental pollutant released by material outgassing and industrial activity. This group of chemicals is particularly difficult to measure because it includes thousands of individual species at only trace concentrations (ppb to ppt level) in the atmosphere. Researchers and regulatory authorities have been challenged to develop new analytical techniques that can keep up with the ever-broadening array of PFAS contaminants and their environmental degradation products. 

Researchers with the US Environmental Protection Agency characterized a TOFWERK iodide chemical ionization mass spectrometer (API-TOF with I CI interface) as a highly-sensitive and flexible PFAS detector. This instrument was chosen because it allows direct measurement without sample preparation, performs soft ionization to minimize compound fragmentation, and the iodide anion was expected to efficiently form an ion-molecule adduct with the target species.  

Seven PFAS compounds were measured, chosen as representative of important FAS functional group classes. Specifically, 4:2, 6:2, 8:2, and 10:2 fluorotelomer alcohol (FTOH), perfluorooctanoic acid (PFOA), perfluorobutanoic acid (PFBA), and hexafluoropropylene oxide dimer acid (HFPO-DA) were measured.  

The researchers first made a direct headspace measurement of the standard at a 0.33 Hz acquisition rate to confirm the instrument detection, then quantified sensitivity by placing a droplet of a diluted solution onto a filter in front of the instrument. The instrument is extremely sensitive: detection limits for a 3-second averaging time were found to be in the single-digit part-per-trillion range. With a 1-minute averaging time, detection limits could be as low as 360 parts-per-quadrillion (0.36 ppt).  

The authors demonstrated the instrument capability by measuring several commercial fluoro products (Masurf FS-115, Zonyl FSA, Capstone FS-35, and Arctic 3 AFFF). In addition to several of the tested substances, a number of compounds with high molecular weight were detected, with enhancement patterns indicative of PFAS compounds. The researchers used the TOFWERK mass spectrometry data analysis package (Tofware) to determine the chemical composition of eleven of these non-targeted PFAS, and highlight that this is a valuable step in identifying a newly detected compound.

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Emerging Contaminants Applications